EP0279321A2 - Co-extrusion head - Google Patents

Abstract

The previously known co-extrusion heads are suitable only for processing thermally stable polymer melts, such as for example PP and PE, because they can be moulded into tubes on manifold sleeves having the known heart-shaped groove distributions. Thermally sensitive polymers, such as for example PVDC and PET, but in particular rigid PVC, cannot be processed in the known co-extrusion heads, since the material would stagnate in the transitional area of the open manifolds and decompose within a short time due to the effect of heat. The co- extrusion head according to the invention also permits the processing of, for example, rigid PVC by a combination of the mandrel support principle, by which a rigid PVC strand introduced into the extruder head at the top is formed into a tube, with the heart-shaped groove principle, by which material strands of another material introduced into the interior of the rigid-PVC tube are processed, for example to form a barrier layer tube and to form adhesion promoter layer tubes. <IMAGE>

Description

The invention relates to a coextrusion head for producing a plastic tube structure consisting of at least two, preferably three to six layers, the outer layer and inner layer of which are made of a thermally sensitive material, e.g. Hard PVC exist, between which either a further layer of this material as a middle layer or one or more layers of other material such as a barrier layer, adhesion promoter layers and regenerate layer can be arranged.

In plastic blow molding technology, multilayer hose structures, the structure of which is adapted to the intended use of the object to be produced, have been state of the art for some time. These multilayer tube structures are produced in coextrusion heads, in which the individual tubes of the tube structure to be produced are first formed and then brought together before the finished tube structure leaves the coextrusion head through a nozzle.

In the previously known coextrusion heads, only thermally stable plastic melts, such as PP and PE, and, if appropriate, associated adhesive and barrier layers are processed, these thermally stable melts being introduced into the extrusion head from the side and on so-called "heart curves" with channels open on one side on quills or distribution sleeves are distributed and formed into hoses. These known coextrusion heads are not suitable for processing thermally sensitive plastic materials, since such material stagnates in the transition region of the open channel to the neighboring component and is quickly affected by the influence of heat Would decompose time. In order to produce a hose from such a plastic, it must be guided axially against a mandrel which distributes the strand to the desired hose.

The thermally sensitive materials include in particular the physiologically harmless rigid PVC, but also e.g. PVDC and PET. EVAL, which is preferably used as a barrier layer for coextrusion, actually belongs to this group. In known coextrusion heads, it can only be processed without difficulty if it forms a very thin internal layer which does not come into contact with hot walls in the head, as is usually the case when processing as a barrier layer. Since rigid PVC is a preferred application example, reference is made only to this in order to simplify the illustration.

The present invention is based on the object of specifying a coextrusion head with which thermally unstable, sensitive material, in particular rigid PVC, can also be processed in multiple layers alone or together with other material, with which e.g. either a hose structure consisting of two or preferably three hard PVC layers or one whose outer layer and inner layer is made of hard PVC can be produced, further layers, in particular a barrier layer with adhesive layers on both sides and optionally a regenerated layer, being arranged between these carrier layers.

This object is achieved by the features specified in the characterizing part of patent claim 1. Advantageous developments of the invention are characterized in the subclaims.

In the coextrusion head according to the invention, a rigid PVC strand is fed into the coextrusion head from above in a central channel and formed into a tube on a mandrel, which at least forms the outer layer of the tube structure to be produced. Another strand of material is fed to the side of the coextrusion head and enters the head through a channel to within the outer layer tube and without affecting its formation. The channel can penetrate a bridge in a mandrel holder. Here, the introduced strand of material can be distributed in a suitable manner and formed into one or more hoses, which are then brought together with the outer layer hose.

If the hose structure to be produced consists of several hard PVC layers, both the material strand for the middle layer and that for the inner layer can be fed into the coextrusion head in side channels. The formation is then advantageously made such that the channel for the material strand of the middle layer leads through a bridge in the upper region of the upper mandrel that holds it to the center of the head, where the strand is formed from a central mandrel into a tube, while the channel for the material strand the inner layer leads through a second bridge, which bridges both hoses present there in the upper area of the middle mandrel, to the middle of the head, where this strand is formed by a lower mandrel to form the inner layer hose. All three hoses are coaxial with each other.

If, according to a further proposal of the invention, the upper and the middle mandrel each have sleeve-shaped, downward-widening extensions, the three hoses can be spatially separated from one another and can thus be designed without any problems until they are in the nozzle footsteps are united. In such a case, the three hoses usually consist of different PVC materials, for example that of the outer layer of a natural glass clear, that of the middle layer of a mother-of-pearl colored and that of the inner layer of a hard PVC containing regrind.

If the coextrusion head according to the invention, in addition to hard PVC layers, also those made of other, thermally stable plastics, e.g. to form a five-layer hose structure with a central barrier layer and double-sided adhesive layers, it is proposed with great advantage that the upper mandrel is attached to a mandrel holder connected to a circumferential central ring, the central ring carrying an annular cover with a roof-shaped cross section. This ring-shaped cover splits the tube formed on the upper mandrel into two concentric tubes, which form the rigid PVC inner layer and the rigid PVC outer layer of the tube structure to be produced.

In order to insert the material strands for the layers of other material, for example the barrier layer and the adhesive layers between the two hard PVC tubes, without impairing the formation thereof, two lateral channels should be provided by webs in the mandrel holder connecting the mandrel to the housing of the coextrusion head through into the space between the two concentric hoses. In order to form the thin barrier layer hose and the two likewise thin adhesive layer hoses there, it is proposed with great advantage that the radially inner region of the mandrel holder is extended in the direction of the underside of the head and that in this extended ring section a distribution channel in the form of a heart curve to form the inner one Adhesive layer hose milled is. A sleeve package consisting of three sleeves is pushed onto this extended ring section, the inner and the middle sleeve each having a distribution channel milled into their outer surface, again in the form of a heart curve, and the distribution channel of the inner sleeve forming the barrier layer tube and the distribution channel the middle sleeve serve to form the outer adhesive layer hose. The outer sleeve covers the middle sleeve and at the same time serves as an inner border for the outer layer hose.

The two lateral channels should initially extend approximately horizontally into the interior of the coextrusion head and be deflected vertically approximately in the middle of the mandrel holder, so that their axes lie in the contact area of the inner and the middle sleeve. The lower end section of the channel leading the material strand for the adhesive layers is so branched that the branches open into the associated distribution channels, while the channel leading the material strand for the barrier layer opens directly into the associated distribution channel.

In this embodiment of the invention, the rigid PVC is first fed as a full strand into the top of the coextrusion head by an extruder and flows centrally against the upper mandrel, through which a hose is produced, which strikes the tip of the roof-shaped ring and is split into two concentric hoses becomes. Between these two hoses, hoses are formed in the form of heart curves from the laterally supplied material strands for the barrier layer and the adhesive layers. In the lower area of the sleeve package, these inner layers are combined with the outer PVC layers and designed as a tube structure consisting of five layers from the coextrusion head.

According to a further proposal of the invention, the upper mandrel of the coextrusion head can be a double mandrel with an upper pointed cone, which flows from above through the central channel, and a second, lower pointed cone, which is flowed from a strand of material which is also led from bottom to top in a central channel. On this double mandrel, further material flows are formed into a tube each, the material flow leading from bottom to top being deflected downward in the molding process and later combined with the same in the same direction of flow as that of the tube outer layer. The upper and lower pointed cones are arranged coaxially with each other.

To form the inner hose layer, an inner inflow ring is arranged coaxially within the double mandrel, the central through hole of which forms the lower central channel through which the material strand is guided upward against the lower pointed cone. The hose layer is formed between the outer wall of this inner inflow ring and the spaced inner wall of the double mandrel.

The double mandrel provided according to the invention enables the formation of two hose layers made of a thermally sensitive material such as e.g. Hard PVC with a small space requirement, the coextrusion head furthermore having only a small number of components. The coextrusion head according to the invention is also particularly favorable with regard to process engineering and its production.

According to the present invention, it is further proposed that the coextrusion head have a core holder plate, which establishes the structural connection between the head housing and all internal components. This applies not only to the double mandrel, which is on a center ring of the core holder plate, and the inner inflow ring, which is held in the central region of the core holder plate, but also for a center ring outlet arranged below the core holder plate or a distributor sleeve package arranged instead, and for an inner core holder or core.

The hose layers formed on the double mandrel are guided downward through ring channels in the core holder plate, these ring channels delimiting the central ring of the core holder plate, which is connected to the adjacent regions of the core holder plate by web bridges. All internally required strands of material are passed through these web bridges, their flow channels being deflected in the correct position within the core holder plate.

If a hose structure consisting of three layers, preferably three PVC layers, is to be produced with such a coextrusion head, a further channel is formed in the core holder plate, which leads a material strand fed laterally into the coextrusion head to the center of the core holder plate and deflects down there where the strand of material hits the upper cone of another mandrel, which is arranged below the core holder plate and forms the inner tube layer.

If, instead of the center ring outlet, a sleeve package consisting of four sleeves is arranged on the underside of the center ring of the core holder plate, the coextrusion head according to the invention can be used to produce a tube structure consisting of five layers, which consists of the outer and inner layer formed on the double mandrel from a thermally sensitive material as well as a central barrier layer with two adjacent adhesive layers. The strands of material fed to the core package become in turn fed into lateral channels of the core holder plate, guided through web bridges into the central ring of the core holder plate and diverted downward there for entry into the respective distribution channels.

A tube structure consisting of six layers can be produced with the coextrusion head according to the invention if the head described above for producing a five-layer tube structure additionally has the simple mandrel arranged below the core holder plate, which is also used in the production of a tube structure consisting of three layers . In the production of a tube structure consisting of six layers, the strand of the regenerated layer is divided into the desired tube at the bottom of the double mandrel, while the inner layer, which is preferably made of PVC, is formed on the lower mandrel. The barrier layer and the two adjacent adhesive layers are in turn formed between the sleeves of the sleeve package.

The double mandrel arranged according to the invention, around which plastic material flows around the entire surface on both sides, ensures problem-free shaping of two single strands into two hose layers, which can of course consist of different materials, with minimal space requirement. The core holder plate further arranged according to the invention not only supports the mandrel, but also establishes the structural connection between the head housing and all internal components, that is to say also a lower mandrel or core and the associated core holder. In addition, the core holder plate contains the feed channels for all the strands of material required internally.

• Fig. 1 einen schematischen Längsschnitt durch einen er­findungsgemäßen Coextrusionskopf;
• Fig. 2 einen schematischen Längsschnitt durch eine zweite Ausführungsform des erfindungsgemäßen Coextrusionskopfes;
• Fig. 3 einen Schnitt entlang der Linie III-III in Fig. 2;
• Fig. 4 einen Schnitt entlang der Linie IV-IV in Fig. 2;
• Fig. 5 einen schematischen Längsschnitt durch eine dritte Ausführungsform des erfindungsgemäßem Coextrusionskopfes zur Herstellung einer aus drei Schichten bestehenden Schlauchstruktur;
• Fig. 6 einen schematischen Länsschnitt durch eine vierte Ausführungsform des Coextrusionskopfes zur Herstellung einer aus fünf Schichten be­stehenden Schlauchstruktur und
• Fig. 7 einen schematischen Längsschnitt durch eine fünfte Ausführungsform des Coextrusionskopfes zur Herstellung einer aus sechs Schichten be­stehenden Schlauchstruktur.

Further features, advantages and details of the invention result from the following description of three preferred embodiments and from the drawing. Show:

• 1 shows a schematic longitudinal section through a coextrusion head according to the invention;
• 2 shows a schematic longitudinal section through a second embodiment of the coextrusion head according to the invention;
• 3 shows a section along the line III-III in Fig. 2.
• Fig. 4 is a section along the line IV-IV in Fig. 2;
• 5 shows a schematic longitudinal section through a third embodiment of the coextrusion head according to the invention for producing a tube structure consisting of three layers;
• 6 shows a schematic longitudinal section through a fourth embodiment of the coextrusion head for producing a tube structure consisting of five layers and
• 7 shows a schematic longitudinal section through a fifth embodiment of the coextrusion head for producing a tube structure consisting of six layers.

In the center of the housing 1 of the coextrusion head shown in FIG. 1, three mandrels 2, 3 and 4 are arranged one above the other in such a way that their longitudinal axes coincide with the longitudinal axis of the housing. The three mandrels are held in the housing by mandrel holders in the form of bridge bridges which allow the plastic material to flow through them. The upper mandrel 2 is held in the housing 1 via an upper bridge 5 and a middle bridge 6, while the middle mandrel 3 is held in the upper mandrel 7 by a middle skeg bridge 7 and the lower mandrel 4 is held in the middle by a lower bridge 8 Mandrel 3 are held.

In order to form a tube structure consisting of three rigid PVC layers, the material for the outer layer is fed in a central channel 9 at the top into the coextrusion head and strikes the tip cone of the upper mandrel 2 as a strand of material, as a result of which it is formed into a tube. The material for the middle layer is introduced through a lateral channel 10, which leads through the bridge 5 to the center of the extrusion head, where the Ka nal 10 is deflected vertically downwards. Here the strand of material meets the tip cone of the central mandrel 3 and receives its tubular shape.

The material for the inner layer is guided through a side channel 11, offset by 180 °, through the two bridge bridges 6 and 7 into the center of the head, where the strand of material is deflected vertically downwards and strikes the lower mandrel 4 vertically from above, which is the Inner layer tube forms.

The upper mandrel 2 and the middle mandrel 3 have sleeve-shaped extensions 12 and 13 which, in the example shown, initially expand downward and reduce their diameter again near the nozzle. They extend up to the vicinity of the nozzle inlet area 14, so that the three hoses are routed separately up to that point and can form freely. The ends 12ʹ and 13ʹ of the sleeve-shaped extensions, which run obliquely inwards in the direction of the sleeve axes, bring the layers together in the nozzle inlet area 14. The influence of the web bridges, which affects the uniform formation of the hoses, is limited to the immediate vicinity of the holding webs forming the bridges and is eliminated in the area of the union of the hoses.

In the coextrusion head shown in FIG. 2, a hard PVC strand is in turn introduced into an upper central duct 15, which adjoins an extruder (not shown), where the strand meets an upper mandrel part 16, which forms a hard PVC hose. This hard PVC hose then meets an annular cover 17, which is roof-shaped in cross section, and which sits on a mandrel holder 18 holding the mandrel in the housing, through the central hub part of which the bolt 20 connecting the upper mandrel part 16 and the lower mandrel part 19 passes. The roof shaped cover 17 divides the hose into an outer layer and an inner layer hose.

As can be seen from FIGS. 1 and 3, the inner hub 21 of the mandrel holder 18 is connected via webs 22 to its central part 18ʹ, which in turn connects the central part to the outer ring 18ʺ via webs 23. The complete mandrel holder 18 is held in a recess in the housing 24 of the coextrusion head.

A lateral channel 25 for feeding the strand of material for an inner layer, e.g. coming from an extruder, e.g. the adhesive layer, and a channel 26 arranged offset by 180 ° for feeding the strand of material for a further inner layer, e.g. the barrier layer, extend horizontally through the outer webs 23 and are deflected vertically downward in order to open into distribution channels 27, 28 and 28.

The mandrel holder 18 has on its underside an elongated ring section 30 into which the distributor channel 28 is milled in the form of a heart curve. Three concentrically arranged sleeves 31, 32 and 33 are pushed onto this ring section 30, the distribution channels 29 and 27 being milled into the outer surfaces of the sleeves 31 and 32. The outer sleeve 33 covers the middle sleeve 32 and also serves to guide the outer layer tube. The sleeves 31 to 33 are fastened to the ring section 30 by screws.

The channel 25 branches in the area of the inner and middle sleeves 31, 32 and opens into the distribution channels 27, 28, as can also be seen from FIG. 4. The lateral channel 26 opens into the distribution channel 29.

The hoses formed in this way are brought together and united at a common opening 34, where the barrier layer and the two adhesive layers are received between the two rigid PVC layers before the hose structure exits the coextrusion head through the nozzle 35.

The coextrusion head shown in FIG. 5 has a double mandrel 37 in the center of the housing 36 with an upper pointed cone 38 and a lower pointed cone 39, which are formed coaxially to one another. An inner inflow ring 49, which delimits the lower central channel 41, is arranged coaxially to the inside of the double mandrel 37, through which a strand of material is guided against the lower pointed cone 39 and is divided there into a hose which is between the inner inflow ring 40 and the double mandrel 37 The upper pointed cone 38 divides a strand of material that is fed through an upper central channel 42.

The double mandrel 37 is supported all around on a central ring 43 of a core holder plate 44, which also holds the inner inflow ring 40. The center ring 43 is connected to the adjacent sections of the core holder plate 44 by web bridges (not shown in the figure).

Through these web bridges, two lateral channels 45 and 46 lead to the center of the core holder plate 44, where the channel 45 is deflected upwards and opens into the lower central channel 41, which guides its strand of material against the lower pointed cone 39. The channel 46 is deflected downwards in the center of the core holder plate 44 and guides its material strand against a pointed cone 47 of the inner core holder 48, on which the inner layer 49 of the tube structure consisting of three layers is located is posed. The inner layer 49, like the two layers 50 and 51 formed on the double mandrel 37, is made of a thermally unstable material. The two layers 50 and 51 are brought together at the lower end of a central ring outlet 52 adjoining the central ring 43 of the core holder plate 44 before they merge with the inner layer 49 to form the three-layer tubular structure.

In FIGS. 6 and 7, those components which correspond to components in FIG. 5 are identified by the same reference numerals. In the extrusion head shown in FIG. 6, the middle ring outlet 52 is replaced by a sleeve package consisting of four sleeves 53-56, which connects to the underside of the middle ring 43 of the core holder plate 44. Instead of the lower mandrel 48, a core 47 is arranged, which is also connected to the core holder plate 44. Lateral channels 58-60 are formed in the core holder plate 44 for the supply of material strands to the sleeve package 53-56, which pass through web bridges into the central ring 43 of the core holder plate and are deflected downward there for entry into distribution channels 61 to 63. In the embodiment of the coextrusion head shown in FIG. 6, a tube structure consisting of five layers is produced, which has an outer layer 50 and an inner layer 64 made of a thermally sensitive material as well as a central barrier layer 65 with adhesive layers 66 and 67 adjoining it.

The coextrusion head shown in FIG. 7 contains, in addition to that according to FIG. 6, the lower mandrel or, as already known from the embodiment according to FIG. Core holder 48a, the pointed cone 47a of which divides the strand of material fed through the lateral channel 46a into a tube 49a forming the inner layer. In this embodiment, the lower pointed cone 39 of the double mandrel 37 divides the regenerated layer strand into a hose 68, which is brought together with the hose 49a. As in the previous exemplary embodiment, a central barrier layer 65 and the double-sided adhesive layers 66 and 67 are formed between the sleeves 53-56. The outer layer 50 and the inner layer 49a in turn consist of a thermally sensitive material.

Claims (23)

1. Coextrusion head for producing a plastic tube structure consisting of at least two, preferably three to six layers, the outer layer and inner layer of which are made of a thermally sensitive material, for example hard PVC, between which either a further layer of this material as a middle layer or one or a plurality of layers of other material, such as a barrier layer, adhesion promoter layers and regenerated layers, can be arranged, characterized in that a first strand of material forming at least the outer layer is fed into a central channel (9, 15, 42) at the top of the coextrusion head and on an upper mandrel (2, 16, 37) is formed into a tube and that at least one further strand of material for at least one further layer in a lateral channel (10, 11, 25, 26, 45, 46, 58, 59, 60) is fed into the head and into the interior of the outer layer hose is guided. 2. Coextrusion head according to claim 1, characterized in that the lateral channel (10, 11, 25, 26) runs through a web bridge (5, 6, 7, 23) in a mandrel holder. 3. Coextrusion head according to claim 1 or 2, characterized in that both the strand of material for the middle layer and the strand of material for the inner layer in side channels (10, 11) are fed into the head. 4. Coextrusion head according to claim 3, characterized in that the channel (10) for the material strand of the middle layer through a first, in the upper region of the upper mandrel (2) connected to this bridge bridge (5) leads to the head center, where the strand of one middle mandrel (3) is formed into a tube, and that the channel (11) for the material strand of the inner layer through two further web bridges (6, 7) which bridge the two tubes and are arranged in the upper region of the middle mandrel (3), leads to the center of the head, where the strand is formed into a tube by a lower mandrel (4). 5. Coextrusion head according to claim 3 or 4, characterized in that the two lateral channels (10, 11) are arranged offset by 180 °. 6. Coextrusion head according to one of claims 3 to 5, characterized in that the upper and the central mandrel (2,3) have sleeve-shaped extensions (12, 13) which bring the hoses together in the nozzle entry region (14). 7. Coextrusion head according to claim 1, characterized in that a mandrel holder (18) an upper has an annular cover (17) which is roof-shaped in cross section and which splits the hose into two concentric hoses which form the inner layer and the outer layer of the hose structure to be produced. 8. Coextrusion head according to claim 7, characterized in that outer webs (23) the central part (18ʹ) of the mandrel holder (18) with its, the mandrel (16, 19) in the housing (24) of the coextrusion head holding outer ring (18ʺ ) connect and that two lateral channels (25, 26), which feed the material strands for the inner layers, eg barrier layer and adhesive layers, extend through the webs (23) into the space between the two concentric tubes. 9. Coextrusion head according to claim 8, characterized in that the radially inner region of the mandrel holder (18) is extended in the direction of the underside of the extrusion head and that in the extended ring section (30) a distribution channel (28) in the form of a heart curve to form an inner Layer, for example an adhesive layer hose is molded. 10. Coextrusion head according to claim 9, characterized in that a sleeve package consisting of three sleeves (31, 32, 33) is pushed onto the elongated ring section (30), the inner and middle sleeves (31, 32) each having one in their Have the outer surface molded distribution channel (29,27) in the form of a heart curve and the distribution channel (29) of the inner sleeve (31) for the formation of a barrier layer hose and the distribution channel (27) of the middle sleeve (32) for the formation of an outer bonding agent layer hose serve. 11. Coextrusion head according to claim 10, characterized in that the outer sleeve (33) covers the middle sleeve (32) and at the same time forms the inner boundary for the outer layer tube. 12. Coextrusion head according to one of claims 1 and 7 to 11, characterized in that the two lateral feed channels (25, 26) initially extend horizontally from the outside inwards and are deflected vertically approximately in the center of the mandrel holder (18), such that their axes lie in the contact surface of the inner and middle sleeves (31, 32). 13. Coextrusion head according to claim 12, characterized in that the two lateral feed channels (25, 26) are arranged offset from one another by 180 °. 14. Coextrusion head according to one of claims 8 to 13, characterized in that the lower end section of the channel (25) leading the material strand for the adhesion promoter layers branches in such a way that the branches open into the distributor channels (27, 28) during which the material strand for the barrier layer leading channel (26) opens into the distribution channel (29). 15. Coextrusion head according to claim 1, characterized in that the upper mandrel is a double mandrel (37) with an upper pointed cone (38) of the in the upper central channel (42), the outer tube layer (50) forming the strand of material and a lower pointed cone (39), which is flown by a strand of material guided in an opposite direction in a lower central channel (41), the double mandrel (37), both material flows to a hose (59, 51, 64, 568 each ) and the material flow from bottom to top is already in the molding process on the double mandrel (37) is deflected downwards before it merges with the other material flow. 16. Coextrusion head according to claim 15, characterized in that the upper and the lower pointed cone (38, 39) are arranged coaxially to one another. 17. Coextrusion head according to claim 15 or 16, characterized in that the lower central channel (41) is guided upwards centrally by an inner inflow ring (40) which is arranged coaxially within the double mandrel (37), the inner tube layer (51 , 64) is formed between the outer wall of the inner inflow ring (40) and the inner wall of the double mandrel (37). 18. Coextrusion head according to one of claims 15 to 17, characterized in that the double mandrel is supported all around on a central ring (43) of a core holder plate (44) on which the inner inflow ring (40) is held. 19. Coextrusion head according to one of claims 15 to 18, characterized in that the two hose layers (50, 51) through the core holder plate (44) and then between a bottom of the central ring (43) of the core holder plate (44) adjoining central ring outlet (52) and the head housing (36) on the one hand and a core (57) or core holder on the other hand, before they join at the lower end of the center ring outlet (52). 20. Coextrusion head according to one of claims 15 to 19, characterized in that the material strand for the lower central channel (41) is fed into a side channel (45) lying in the core holder plate (44) in the coextrusion head, the channel (45 ) leads through web bridges to the center of the core holder plate (44) and is deflected there upwards. 21. Coextrusion head according to one of claims 15 to 20, characterized in that a sleeve package consisting of four sleeves (53-56) is arranged on the underside of the central ring (43) of the core holder plate (44) and that the inner three sleeves (53- 55) each have a distribution channel (61-6) shaped into their outer surface in the form of a heart curve and form a central barrier layer (65) and adjacent adhesive layers (66, 67), which are formed between the layers (50, 64) formed on the double mandrel (37) ) guided and brought together with these at the lower end of the sleeves (53-56). 22. Coextrusion head according to claim 21, characterized in that the material bundle supplied to the sleeve package (53, 56) in the core holder plate (44) lying in the side channels (58-60) fed into the coextrusion head, by web bridges in the central ring (43) Core holder plate (44) and there diverted downwards for entry into the respective distribution channel (61-63). 23. Coextrusion head according to one of claims 15 to 22, characterized in that a further strand of material in a side channel (46, 46) lying in the core holder plate (44) is fed into the coextrusion head, guided through web bridges to the center of the core holder plate and down there is deflected, whereupon the material strand on the upper pointed cone (47, 47a) of a mandrel (48a) arranged coaxially to the double mandrel (37) below the core holder plate is formed to form the inner tube layer (49, 49a).

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